Waste Minimization Strategy: Flexible Polyurethane Foam Manufacture

Methylene chloride and CFCs are used as auxiliary blowing agents in the manufacture of flexible polyurethanefoams and are promptly emitted during the manufacturing processes.The concentrationof the auxiliary blowing agent are quite low due to the accepted practice of using large volumes of air to lower the ambient concentration of toxic isocyanates (a key chemical in the urethane reaction sequences). The manufacturing process was simulated in the laboratory. The magnitudes and rates of auxiliary blowing agent loss were quantified and related to stages in the foam blowing operation. These data were validated with analogous measurements at foam plants. A mathematical model was developed to predict tunnel auxiliary blowing agent concentrations as a function of formulation, tunnel length, conveyor speed, and air flow. A strategy was developed to isolate the foaming tunnel (where approximately 60% of emissions occur) and decrease the air flow to increase the tunnel (and stack) concentration of methylene chloride. This isolation/ concentration strategy is expected to improve the economics for recovery/reuse of the auxiliary blowing agent while minimizing worker exposure to isocyanates. This strategy will be tested in a flexible polyurethane foam plant in 1991 with a slipstream of emitted methylene chloride recovered using Brayton Cycle technology. Characterization of recovered methylene chloride as well as product qualities over a range of foams is planned. The use of environmentally benign materials (natural products) as substitutes for halogenated organic auxiliary blowing agents was investigated. A series of laboratory foams were prepared using solid carbon dioxide, limonene (from citrus trees), pinene (from pine trees), and isoprene (from a variety of deciduous vegetation) as alternative auxiliary blowing agents. While success was limited with dry ice-blown and terpene-blownfoams, isoprene-blownfoams exhibited excellent denslty reductions and physical properties. Additional experimentation needs to be conducted on isoprene-blown foams over a wide range of product formulations. Although isoprene is currently regulated as a VOC, it is naturally emitted in large quantities by deciduous vegetation; a literature survey needs to be completed to document the magnitude of natural emissions and the accepted technologies for control of anthropogenic emissions.